This invention relates an optical fiber wavelength multiplexer-demultiplexer or router, liable to be used as a component in optical fiber teletransmission installations.
Such multiplexers-demultiplexers are already known; they have been described, then gradually improved, especially in the French patents FR-2.543.768, FR-2.519.148, FR-2.479.981, FR-2.496.260 and in the European patent EP-0.196.963.
The latter document relates more particularly to a multiplexer-demultiplexer in which the input and output fibers are positioned at the immediate vicinity of the focus of a concave mirror. Thus, the diverging light fluxes received from the input fibers are transformed by the concave mirror into parallel light beams which are addressed to a plane diffraction grating, which directs the parallel beams back to the concave mirror and focuses them onto the extremities of the output fibers.
We have sought to reduce the aberrations and, in particular, the spherical aberrations of such a system and it is thus that such a multiplexer-demultiplexer has been suggested, comprising a fiber-holder element, an element carrying the diffraction grating, an intermediate element and a spherical mirror element. The fiber-holder element puts the extremities of the fibers in contact with the element carrying the diffraction grating, the intermediate element which is in contact with the diffraction grating and has the same optical index as the element which carries it, is terminated by a spherical face which is in contact with the mirror.
This device has proven satisfactory, has enabled and still enables numerous embodiments.
However, in certain particular applications, this component has appeared regrettably relatively heavy, as well as its thermal instability produced by the index variation of the different elements of which it consists, in relation to temperature.